Volume Viewer: move classes to non-default package

The reason is that classes in the default package take silent precedence
over classes made available via wildcard imports, which has caused
confusion on multiple occasions.

For example, the statement "import java.awt.*;" does *not* import the
java.awt.TextField class when a packageless "TextField" class is also on
the classpath.

See this thread for further rationale and discussion:
https://groups.google.com/d/msg/fiji-devel/6Ua05iccSVo/5ZLrUO-FhmUJ
Added barycenter of sampled profile (linear Sholl)
Updated documentation link
Minor cleaning
v3.1: Retrieve multiple plots at once
Made prompt intuitive, use DialogListener instead of individual listeners, Added "Batch mode" option, Output profiles to a single table
Updated Release Notes
Corrected PMD warnings
Perform linear regression with percentiles 10-90
General fixes. Plot improvements
Fixed mis-assignment of booleans in prompt.
Adjusted details of sample image
Fixed mis-assignment of booleans in prompt.
Adjusted details of sample image
Merge
Do not reinvent the wheel and use addCheckboxGroup()
when building dialog
Ensure summary table is updated upon linear regressions
Added normalization against annulus
Log simplex details for both Semi-log regressions when in verbose mode
Apply linear regressions to Log-log method, since the exponential with offset is not intuitive
Saving files: Do not record path of saved images.
Removed extra File.separator from target directory
Try to guess the polynomial of best approximation
Analyze profiles obtained elsewhere, including Simple Neurite Tracer
Tabular data: keep track of imported table
Enclosing radius is defined by a specified cutoff value.
Removed the "Sholl LUT" command, deprecated since IJ 1.48a.